The present invention relates to a drilling device for producing drilled holes with undercuts.
More particularly it relates to a drilling device which has a depth stop and a suction bell arranged on the depth stop.
Devices of the above mentioned general type are known in the art. One of such drilling devices is disclosed, for example in the German reference DE 3,835,025. In the drilling device disclosed in this reference the drilling dust accumulated during the operation of drilling and reaming out the undercut can be discharged through an axial through-bore of the drill shank. This drilling device also has an enlargement of the drill shank acting as a swivel bearing. The device also has a depth stop. When the depth stop is positioned on the outer surface of the masonry, the drill bit axis is swivelled out using the enlargement as the swivel point, until the tapered parts of the drill shank engage a wall of the drilled hole. In this swivelled-out position, by a gyratory movement the undercut is reamed out at the bottom of the drilled hole.
In the above described known drilling device the drill bit and the drill bit chuck are joined to one another by means of a thread, and the suction bell is rotatably mounted between the above two parts. A collar molded integrally with the drill shank acts as the depth stop. During contacting the wall surface it strikes against it and can cause the mouth of the drilled hole to break open. This occurs particularly during the swivelling operation because the inclined position of the drill bit axis causes the collar to lie lopsidedly against the surface of the masonry. Besides causing the damage to the masonry surface, the hard and lop-sided impacts may also damage the drilling device, in particular the threaded connection between the drill bit and the drill bit chuck.